Dear Fred, Just wanted to let you know what I'm up to. After the various pressing chores, etc., that had accumulated over my month away, my monthly crossword editing job came (and went -- it's now over). In all of this I've been studying the 11-cell in my free time. Partly reading Coxeter's detailed paper, partly making a lot of little sketches. Don't know if I'll ever get to the point of being able to visualize it in one mental picture. But at least I have a good sense of what the neighborhood of a vertex looks like. So that when I return to your manuscript, I will feel that I have a good grip on what we're talking about -- so I can see what happens when one icosa/2 has the interiors of all its triangles removed. (Part of my visualization problem is that the 11 (icosa/2)'s fit together like the graph K_11, aka the 1-skeleton of the (say regular) 10-simplex. Which like any regular k-simplex (without its one k-dimensional cell) naturally sits in the (k-1)-sphere . . . so K_11 naturally sits in the 9-sphere. And I'm not that familiar with visualizing the 9-sphere! --Dan Sometimes the brain has a mind of its own.